A Smurf hat is a piece of clothing generally worn by all Smurfs. It resembles a standard woolen cap with the top part of it flopping forward (or in any preferred direction, as with Slouchy's hat). Male Smurfs generally wear Smurf hats because the top of their heads are bald. Female Smurfs tend to wear them simply to identify themselves as Smurfs.
Smurf hats may also vary in appearance depending on the type of Smurf wearing it. Greedy, who is the village chef, wears a Smurf hat that is a variation of a chef's hat.
In Vic George's series of Smurfs fanfiction stories, there is a musical band in the village called Smurfs Without Hats, so named due to the Smurfs in the band not wearing hats. Also, Sassette in those stories has forgone the use of a hat in favor of wearing a ponytail with a big pink ribbon.